Effective use of both continuous wave (CW) and pulsed directed electromagnetic beam devices (most notably lasers) requires diagnostic information on the beam. Valuable information typically includes the spatial profile, total energy, beam arrival time, duration of exposure, and the variation of these physical parameters throughout an irradiation experiment or use.
Previously, several methods have been used to supply diagnostic information on laser beams. In one method, a plexiglass plate is placed in the target position and irradiated. The mass removed by vaporization is directly proportional to the incident laser energy; the shape of the burn pattern or crater is analyzed to obtain both the spatial distribution and peak-to-average intensity ratio. The disadvantages inherent in this method are nonconcurrence with target testing (laser parameters can and often do vary widely and unpredictably during an experiment), high cost, and questionable accuracy and usefulness for pulsed lasers. In another method, laser radiation is directed into a calorimeter to obtain the total energy of the beam. Calorimeters are used to calibrate plexiglass data as well as scanner data. In the CW case the whole beam is directed into the calorimeter; in the pulsed case only part of the beam is directed into the calorimeter. The disadvantages of that method include nonconcurrency with target testing when the whole beam is used, high cost, and only partial use of the beam in some applications. Another method employs scanners. These devices view the front surface of a mirror. The scanner detector records the diffusely scattered light from the spot. These scanners are used to obtain the spatial distribution of the radiation on a target. The disadvantages of that method include non-concurrency with target testing, complex instrumentation and long set-up times, incompatibility with pulsed lasers because the scan rate is not fast enough, cost and the crucial dependency of the devices on the surface condition of the mirrors.